1. Field of the Invention
The present invention relates to a sheet after-treatment device for performing after-treatment on sheets and to an image forming apparatus equipped with the sheet after-treatment device as a component. In particular, the present invention relates to a sheet after-treatment device allowing a reduction in size without impairing sheet transport and to an image forming apparatus equipped with such a device.
2. Related Background Art
Conventionally, a sheet after-treatment device is provided, for example, in the main body of an image forming apparatus as one of the components of the image forming apparatus, to perform after-treatment on a sheet with an image formed thereon transported from the apparatus main body. The image forming apparatus, which forms an image on a sheet, may consist of a copying machine, a printer, a facsimile apparatus, or a multifunction apparatus consisting of a combination of such apparatuses. The sheet, on which an image is to be formed, may consist of an ordinary paper sheet, a thin sheet of resin which is an ordinary paper substitute, a cardboard, a postcard, a sealed letter, a sheet for an overhead projector or the like.
Conventionally, a sheet after-treatment device provided in the main body of an image forming apparatus aligns the end portions of a plurality of sheets which have undergone image formation (printing) and performs an after-treatment such as stapling.
FIG. 10 shows an example of the construction of a sheet after-treatment device. This sheet after-treatment device, designated by a numeral reference 1000, is equipped with a discharge roller pair 1003 constituting a sheet discharge outlet, an intermediate stacking surface 1002 on which the discharged sheets are stacked together, a stapler 1001 arranged on the opposite side with respect to the sheet transport direction indicated by the arrow E, etc. The sheets discharged from the discharge roller pair 1003 are stacked on the intermediate stacking surface 1002, and undergo switch-back transport in the direction indicated by the arrow F toward an opening 1001a of the stapler 1001. Then, while their ends in the direction intersecting the sheet transport direction (i.e., the width direction) and their ends in the sheet transport direction are being aligned, the sheets are introduced into the opening 1001a. Then, the stack of sheets SB is stapled by the stapler 1001 before being discharged to the left as seen in FIG. 10.
FIGS. 11A through 11C show another example of the construction of a sheet after-treatment device. As shown in FIG. 11A, in this sheet after-treatment device, designated by a reference numeral 1010, a stapler 1011 is arranged off the sheet transport path so that it may not obstruct the transport of sheets in the direction indicated by the arrow Q.
In the former type of conventional sheet after-treatment device 1000, shown in FIG. 10, in which the sheets, once transported in the direction of the arrow E, are transported backwards in the direction of the arrow F, it is necessary for the intermediate stacking surface 1002 and the stapler 1001 to be arranged at a position one step lower than the discharge roller pair 1003. Accordingly, the sheet after-treatment device 1000 requires extra space in the vertical direction, which leads to a rather large height, resulting in a rather large device size.
In the latter type of conventional sheet after-treatment device 1010, it is necessary to once abut the sheets, which have been transported in the direction of the arrow J (FIG. 11B), against a surface on the opposite side with respect to the sheet transport direction in order to effect alignment in the sheet transport direction. Further, it is necessary to move the sheets from the sheet transport path to the opening of the stapler 1011 as indicated by the arrow G (FIGS. 11A to 11C). Thus, a wide intermediate stacking portion is required, so that the size of the device as a whole becomes rather large. In this case, the stapled sheets are transported in the direction of the arrow Q.
Further, in those conventional sheet after-treatment devices 1000 and 1010, ineffective staples generated as a result of mis-stapling or the like of the staplers 1001 and 1011 can fall to cause short-circuiting in the electrical components. In view of this, it is necessary to provide in the vicinity of the stapler 1001, 1011 a recovery tray for recovering the ineffective staples. However, the provision of the recovery tray requires extra space, resulting in an increase in the general size of the device and in cost.